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cmd/compile: better error when assigning to struct field in map

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Identify this assignment case and instead of the more general error

    prog.go:6: cannot assign to students["sally"].age

produce

    prog.go:6: cannot directly assign to struct field students["sally"].age in map

that explains why the assignment is not possible.

Fixes #13779.

Change-Id: I90c10b445f907834fc1735aa66e44a0f447aa74f
Reviewed-on: https://go-review.googlesource.com/21462
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Caio Marcelo de Oliveira Filho 2016-04-02 11:27:02 -03:00 committed by David Chase
parent 1f5b1b2b66
commit f229e46783
2 changed files with 20 additions and 0 deletions
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5
src/cmd/compile/internal/gc/typecheck.go
View File

@ -3207,6 +3207,11 @@ func checkassign(stmt *Node, n *Node) {
return
}
if n.Op == ODOT && n.Left.Op == OINDEXMAP {
Yyerror("cannot directly assign to struct field %v in map", n)
return
}
Yyerror("cannot assign to %v", n)
}

15
test/fixedbugs/issue13779.go Normal file
View File

@ -0,0 +1,15 @@
// errorcheck
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Issue 13779: provide better error message when directly assigning to struct field in map
package main
func main() {
type person struct{ age, weight, height int }
students := map[string]person{"sally": person{12, 50, 32}}
students["sally"].age = 3 // ERROR "cannot directly assign to struct field .* in map"
}